Thin film conductive and non-conductive coatings on a substrate have many uses in industry, including coatings on flat panel displays, semiconductors, touch screen displays, energy control coatings on glass, and optical interference filters, among other uses.
These films are applied to surfaces in a variety of methods. One commonly used method is referred to as sputter deposition. Typically, in a sputter deposition process, the article to be coated, the substrate, is placed in a chamber. A plate of the material to be used in the coating, called the target, is also placed inside the chamber. The target is electrically connected to a voltage source, and serves as an electrical cathode/target. Typically, the sputtering chamber is evacuated, and a gas under pressure is pumped into the chamber. The gas selected for use in the chamber is dependent upon whether the sputtering process is to be a reactive or non-reactive process. If it is a reactive process, the gas is selected such that it reacts with the material of the target to form the desired material to be sputtered onto the substrate. For non-reactive sputtering, an inert, non-reactive gas is selected.
The target is electrically energized. The electrical field between the anode of the electrical source and the cathode/target will ionize the gas in the chamber. The gas ions are then driven into the target by the electrical field. When this is done with sufficient energy, some of the material is dislodged from the target. The dislodged material typically becomes electrically neutral a short distance from the target, and travels through the chamber from the target to the surface of the substrate. If the process is a reactive sputtering process, the dislodged material reacts with the gas as it is traveling through the chamber and may also be reacted at the surface of the substrate. At the substrate, the target material or reacted target material forms a thin film coating on the surface of the substrate. This method produces a high quality film, but the speed of sputtering must sometimes be very slow to overcome certain problems associated with the sputter deposition process and still maintain a consistent film coating.
There are several problems associated with sputter deposition processes, and in particular with reactive sputter deposition processes. For example, as the material is being sputtered, reactions can occur between the gas in the chamber and the target surface, forming a dielectric layer on the target that can act like a capacitor and cause electrical arcing. The arcing can cause uneven application of material to the substrate and defects in the coating. Varying the voltage applied or the speed at which sputtering is performed have helped reduce the problems and improve the quality of the film coating, but have not been completely successful in achieving all of these goals.
Non-reactive sputter deposition processes are relatively fast. Arcing typically occurs more frequently in reactive sputter deposition processes because reactions between the target material and the gas in the chamber occur more frequently. For this and other reasons, reactive sputter deposition is generally performed more slowly than non-reactive sputtering.
A variety of types of electrical sources have been used in an attempt to reduce or compensate for the electrical arcing that occurs. Electrical voltage sources used have included direct current (DC), alternating current (AC), and radio frequency (RF). While the different electrical sources have been found to reduce the incidence of arcing in certain configurations, there have continued to be problems with the systems. Additionally, with reactive sputtering, the speed at which deposition could be performed is still very slow, which increases the time necessary to produce an acceptable product, and therefore kept costs fairly high.
Therefore, what is needed is a system and method for performing sputter deposition that reduces or eliminates electrical arcing from the target, that does not impact the quality of the film being deposited and minimizes the reduction in speed of coating, especially when reactive sputtering is used.